How to convince the grant secretary
The grant secretary is your first contact within the funding body. His or her duty is to receive your application, process it first to the reviewers and then to a commission. The secretary has to take care of all the paperwork, and therefore has a lot to do, especially when the grant is competitive. Sometimes, they spend as little as 5' to 15' per application before the applications goes either to the reviewers or to the trash bin.
What can you do to avoid the trash bin?
The most important thing that makes the secretary process your application positively is to follow the instructions. Read the grant description very carefully, and stick to it by the letter. For instance, "700 words maximum" means that 705 is too much. "Deadline May 15th" means May 16th is too late already. Counting pages is less work than finding reviewers, so if your secretary has dozens of applications to process, she will first reject all that do not fit the criteria. In some funding rounds, up to 25% of applications are rejected due to formal reasons. So being diligent is a must-have when writing your application.
This does not mean that exceptions are never made. But if you think an exception should be made for your application, it is imperative to get explicit permission for that. Contact the funding body and ask. People in grant agencies generally want to help. After all it is their job to fund researchers. Answering a brief question on the phone is less work than sorting out another application that does not fit the scope.
Conclusion
Read instructions very carefully, stick to the guidelines, and your grant secretary is very likely to wave your application through to the next stage.